After announcing a zero-day vulnerability in Internet Explorer over the weekend, Microsoft has updated its advisory to make the workarounds more clear for enterprises affected. The good news is attacks in the wild only affect versions 9, 10 and 11.

First, let's review the danger. Microsoft reported that an attacker that successfully exploits this vulnerability -- which uses Adobe Flash as a way in -- could gain the same user rights as the computer's user.

"If the current user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability could take complete control of an affected system," Redmond said. "An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights."

Microsoft suggested its Enhanced Protection Mode as a workaround. EPM is a feature found in IE 10 and 11 on 64-bit systems.

The update Tuesday to the weekend security advisory clarifies that EPM will help protect users of Internet Explorer 10 on Windows 7 for x64-based systems, Windows 8 for x64-based systems, and Windows RT, and Internet Explorer 11 on Windows 7 for x64-based systems, Windows 8.1 for x64-based systems, and Windows RT 8.1.

When Will the Madness End?

We caught up with Jeff Davis, vice president of engineering at security solutions firm Quarri Technologies, to get his take on the zero-day flaw. He told us browser vendors will never patch the "last vulnerability," and we'll probably always have to deal with new zero-day drive-by exploits from time to time.

"To give you an idea of the complexity of modern browsers, Chrome and Firefox each have more than 7 million lines of code and average more than 4,000 commits per month," said Davis. "Even if one of them spent three months doing a massive security audit, by the time they finished there would be 12,000 additional changes to review."

On top of that, Davis said, security audits don't pay the bills unless you're the auditor, so patching issues will always be to some extent a reactive process. Given all this, he concluded, purpose-built browser security solutions are a necessity these days for browsers that handle sensitive information.

Who's Most at Risk?

Tyler Reguly, manager of security research at security software firm Tripwire, told us many enterprises users don't have permissions to install alternatives to IE -- so it's gong to continue to be a target for attackers.

"People are overlooking Microsoft's mention of 'limited, targeted attacks.' Exploits for the vulnerability aren't widespread yet and may not become widespread before patches are released," Reguly said.

FireEye is reporting active attacks against companies in the U.S. with ties to the defense and financial sectors. But, ultimately, any enterprise that uses IE is at risk. From Reguly's perspective, this isn't the first time we're hearing about an Internet Explorer zero-day this year and it won't be the last. The solution: make sure that systems have the best possible.

Mitigating the Risk

"The best advice is to ensure all systems have EMET (Microsoft's Enhanced Mitigation Experience Toolkit) deployed and that unnecessary browser add-ons are disabled. This should be part of an enterprise's standard security posture and shouldn't require extra cycles or last-minute deployment," Reguly said. "If companies aren't taking these basic steps to adequately defend their systems by deploying the tools available to them, a new zero-day is probably the least of their concerns."

Reguly's colleague, Tripwire security researcher Craig Young, told us despite the fact that this vulnerability is being actively exploited in the wild, and the Bromium Labs report that many EMET features can be bypassed, users and administrators should not feel helpless.

"EMET may not be perfect but it has been hugely successful at preventing exploitation of zero-day threats," Young said. "If you haven't used it yet, now is a great time to start."